Explosive



United States Patent EXPLOSIVE Byron C. Baldridge, East Alton, 111.,assignor to Olin Mathieson Chemical Corporation, a corporation ofVirginia No Drawing. Application March 25, 1954, Serial No. 418,747

6 Claims. (Cl. 525.1)

This invention relates generally to explosives and more particularly toa novel explosive charge adapted for use in tools such as'oil wellperforated guns.

In the drilling of oil Wells, formations which appear suitable forproducing oil are often by-passed in favor of drilling to greater depthsin the search of more and possibly better formations. Then, after themaximum depth to which the Well is to be drilled has been reached, acasing is inserted into the oil well to the depth of the lowestformation found and the oil is pumped or otherwise removed therefrom.After all of the oil has been recovered from this formation, it is thendesirable to investigate those formations which were by-passed duringthe drilling operation. This is accomplished by forcing projectiles orslugs through the casing and into the surrounding strata by means of oneof the various perfora- 30 tor guns which are available for thispurpose, such as, for example, one similar to the perforator disclosedin U. S. Patent 2,141,827. The projectile is forced from such guns bymeans of an explosive charge. This explosive charge must develop a largeamount of energy when fired in order to force the projectile through thecasing and into the surrounding strata.

Heretofore, the explosives utilized in gun perforators have contained inaddition to nitrocellulose large quantities of nitroglycerine. Suchexplosives under ordinary circumstances outside an oil well will developsuflicient energy to satisfactorily propel a projectile. it has beenfound, however, that such a charge does not develop sutficient energywhen it is fired in a deep oil Well to satisfactorily force theprojectile from the gun perforator through the oil well casing. This isparticularly true if 45 the charge is allowed to remain in the well foran appreciable time before the gun is fired. Frequently, the charge iscapable of forcing the projectile only partially through the casing andas a result the perforator gun becomes lodged in the well. Furthermore,the explosive composition frequently fires prematurely as it is loweredinto the oil well. It is therefore an object of this invention toprovide a novel explosive charge adapted for use in tools. Anotherobject of this invention is to provide an explosive charge havingimproved characteristics in deep oil wells. A further object of thisinvention is to provide an explosive charge for perforator guns whichhas advantageous characteristics under the temperature and pressureconditions ordinarily encountered in deep oil wells.

It has been found that the foregoing objects as well as others areaccomplished, generally speaking, by providing an explosive charge foroil well casing perforators and similar tools composed essentially ofhigh density particles of gelatinized nitrocellulose which has anitrogen content of at least about 12.8 percent. The solidifiedparticles have a surface area within the range of from about 100 toabout 200 square centimeters per gram. The gravimetric density of theparticles must be above about 0.800. Ordinarily, the amount ofstabilizer, moisture, volatiles and like substances do not exceed morethan about percent of the weight of the particles so that the particleis composed of a minimum of about 95 percent nitrocellulose and nosubstances are included which would impair the explosive characteristicsor heat stability of 5 the particles. Suitable stabilizers includediphenylamine, the diphenyl dialkyl ureas and the like in the amounts ofabout 0.7 to about 1.2 percent. The particles are ordinarily coated withfrom about 0.1 to about 0.5 percent by weight graphite.

Contrary to the conventional practice of providing a progressive burningexplosive for forcing projectiles, it has been found in accordance withthis invention that the explosive charge for forcing the projectile froma gun perforator should be a neutral or non-progressive burning charge.The explosive charge must have a fast burning rate and must quicklydevelop a large amount of energy when the charge is fired. In order tomake an explosive having a fast burning rate and one which develops alarge amount of energy, it has been the practice in the art to addsubstantial quantities of nitroglycerine to the explosive charge.Nitroglycerine must be avoided in producing the high energy, highly heatstable charge required for satisfactory performance in an oil well. Anymodifications which would tend to make the particles of smokeless powderprogressive burning should also be avoided. Substantial quantities ofdeterrents, such as for example, dinitrotoluene and dibutylphthalatemust be avoided in order to produce the explosive having the requiredcharacteristics.

Any suitable process for forming fibrous nitrocellulose into gelatinizednitrocellulose particles may be utilized, but an emulsion type ofprocess, for example as disclosed by Schaelfer in U. S. 2,160,626 isadvantageous. In accordance with this invention only those particlespassing through a screen having openings of about 0.015 inch andremaining on a screen having openings therein of about 0.0075 inch areutilized for forming the explosive charge. In order to form dropletswithin the aforesaid size range, agitation of the emulsion must bevigorous.

In most gun perforators, an explosive charge of substantially sphericalparticles is preferred, but digressive burning particles of gelatinizednitrocellulose which have been rolled in accordance with conventionalmethods to flatten the spheres of digressive burning particles of singlebase nitrocellulose formed by other methods are suitable for the purposeand are, in fact particularly advantageous in some perforators.

In order better to clarify and further describe the invention thefollowing is a description of one embodiment thereof:

About 100 parts by weight nitrocellulose composed of about parts 13.4percent nitrogen nitrocellulose and about 40 parts 12.6 percent nitrogennitrocellulose are suspended in about 800 parts water. About 330 partsof a suitable solvent such as ethyl acetate containing about 1 part of astabilizer such as diphenylamine are added to the suspension. About 1part calcium carbonate or other suitable neutralizer is added and theresulting slurry is agitated at about 70 C. until the nitrocellulose hasdissolved and 8 parts gum arabic dispersed in about 50 parts water areadded as agitation is continued. About onehalf hour later about 33 partssodium sulfate dissolved in about 100 parts water are added and theslurry is rapidly agitated for about four hours after which time thetemperature is gradually raised and the solvent is distilled from theslurry. After cooling the resulting solidified droplets are separatedfrom the liquid phase.

Those solidified droplets passing through a screen having openings ofabout 0.015 inch and remaining on a screen having openings of about0.0075 inch are segregated from the remaining droplets by a conventionalwet screening process and are/thereafter dried in a conventional traytype steam heated dryer. These dried droplets are subsequently tumbledin a sweetie barrel with about 0.4 part graphite by means of aconventional coating process. The chemical composition of the resultingparticles of gelatinized nitrocellulose of this embodiment is about:

Percent Nitrocellulose Q 97 Nitrogen in nitrocellulose 13.2Diphenylamine 1 Calcium carbonate 0.5 Moisture 1 Graphite 0.3

The gravimetric density of the droplets is about 0.935. The surface areais about 135 square centimcters per gram.

It has been found that the non-progressive burning explosive charge ofthis invention contrary to the prior explosive charges containingnitrocellulose has not lost any of its energy when fired after it hasbeen exposed to temperatures and pressures encountered in an oil well.Such an explosive is capable of developing as much as 980 caloriesenergy per gram even after an exposure to temperatures as high as 330 F.for the period of time ordinarily required to properly locate theperforator gun in the well. In addition, this charge is capable ofdeveloping high energy without developing excessive and deleteriouspressures within the gun when it is fired. Moreover, such an explosivecharge is not 'only advantageous because it is capable of developing theenergy required to force the projectile through the casing of the oilwell but also because it has a high loading density occupying a minimumamount of space and permitting greater charge weights. Such an explosivecharge is not only useful in perforator guns but is also useful in otherexplosive actuated tools and the like requiring the rapid development oflarge amounts of gas under a variety of environments.

Although the embodiments of the explosive charge of this invention havebeen described in detail in the foregoing many variations within theskill of the art can be made without departing from the spirit and scopeof the invention as set forth in the appended claims.

What is claimed is:

1. As an article of manufacture, an explosive charge of non-progressiveburning single base smokeless powder composed essentially of particlesof gelatinized nitrocellulose having a nitrogen content of at least 12.8percent, said particles having a surface area within the range of fromabout 100 to about 200 square centimeters per gram thereof with eachparticle having dimensions that enable it to pass through a screenopening of 0.015 inch and remain on a screen having 0.0075 inchopenings, and having a gravimetric density of at least about 0.800.

2. An explosive charge composed essentially of solidified substantiallyspherical droplets of gelatinized nitrocellulose having a nitrogencontent of at least about 12.8 percent, said droplets having a surfacearea within the range of from about 100 to about 200 square centimetersper gram thereof with each droplet having dimensions that enable it topass through a screen opening of 0.015 inch and remain on a screenhaving 0.0075 inch openings, and having a gravimetric density of atleast about 0.800.

3. In a device for forcing projectiles through the easing of an oilwell, an explosive charge composed essentially of particles ofgelatinized nitrocellulose having a nitrogen content of 13.2 percent,each of said particles having a surface area within the range of fromabout 100 to about 200 square centimeters per'gram thereof with eachparticle having dimensions that enable it to pass through a screenopening of 0.015 inch and remain on a screen having 0.0075 inchopenings, and having a gravimetric density of at least about 0.800.

4. In a device for forcing projectiles through the easing of an oilwell, an explosive charge of solidified substantially spherical dropletsof gelatinized nitrocellulose having a nitrogen content of about 13.2percent, from about 0.8 to about 1.2 percent stabilizer, a gravimetricdensity of about 0.935 and a surface area within the range of from about100 to about 200 square centimeters per gram thereof with each particlehaving dimensions that enable it to pass through a screen opening of0.015 inch and remain on a screen having 0.0075 inch openings.

5. An explosive charge suitable for forcing projectiles under conditionsincident at the underground levels where oil well casings must beperforated, consisting essentially of a charge of solidified droplets ofgelatinized nitrocellulose having a size such as to pass through ascreen whose openings are 0.015 inch in diameter and tofbe retained on ascreen whose openings are 0.0075 inch in diameter.

6. A non-progressive burning explosive charge adapted to force aprojectile through the casing of an oil well, said charge consistingessentially of particles containing at least about nitrocellulose havinga nitrogen content of at least 12.8 percent, said particles having asurface areaof from about to about 200 square centimeters per gram witheach particle having dimensions that enable it to pass through a screenopening of 0.015 inch and remain on a screen having 0.0075 inchopenings, and a gravimetric density of at least about 0.800.

References Cited in the file of this patent

1. AS AN ARTICLE OF MANUFACTURE, AN EXPLOSIVE CHARGE OF NON-PROGRESSIVEBURNING SINGLE BASE SMOKELESS POWDER COMPOSED ESSENTIALLY OF PARTICLESOF GELATINIZED NITROCELLULOSE HAVING A NITROGEN CONTENT OF AT LEAST 12.8PERCENT, SAID PARTICLES HAVING A SURFACE AREA WITHIN THE RANGE OF FROMABOUT 100 TO ABOUT 200 SQUARE CENTIMETERS PER GRAM THEREOF WITH EACHPARTICLE HAVING DIMENSIONS THAT ENABLE IT TO PASS THROUGH A SCREENOPENING OF 0.015 INCH AND REMAIN ON A SCREEN HAVING 0.0075 INCHOPENINGS, AND HAVING A GRAVIMETRIC DENSITY OF AT LEAST ABOUT 0.800.